Ferroelectric and piezoelectric composition

ABSTRACT

FERROELECTRIC AND PIEZOELECTRIC COMPOSITIONS CONSISTING ESSENTIALLY OF A SOLID SOLUTION OF AN TERNARY SYSTEM     WHEREIN FROM 0 TO 25 ATOMIC PERCENT OF THE PB+2 IS REPLACED BY AN ALKALINE EARTH METAL IS DISCLOSED. THE CONSTITUENTS ARE DEFINED BY THE FORMULA   X+Y++Z=100   WHEREIN X, Y AND Z ARE IN THE FOLLOWING RANGES, TAKEN WITH REFERENCE TO THE FIGURE ABCDEFGH IN FIG. 1: ALSO DISCLOSED IS A BINARY SYSTEM CONSISTING OF FROM 55 TO 75 MOLE PERCENT PB(INNB)0.5O0 AND FROM 45 TO 25 MOLE PERCENT PBTIO3 WHEREIN FROM 0 TO 2K ATOMIC PERCENT OF THE PB+2 IS REPLACED BY AN ALKALINE EARTH METAL.   A 75 0 25 B 60 10 30 C 10 60 30 D 5 55 40 E 5 45 50 F 15 30 55 G 35 10 55 H 55 0 45   X Y Z   X-PH(INNB)0.5O3--Y-(PHZRO3)-Z-(PBTIO3)

June 12, 1973 M|TSUQ QSADA ET AL 3;738,93$

FERROELECTRIC AND PIEZOELECTRIC COMPOSITION Filed March 4, 1971 2 Sheets-Sheet 1 Trio r Compositional Diagram The TernorySysiem Pb(ln Nb )0 PbZrO PbTiO (mol%) 2 2 3 3 3 PbUH ND v 5 H 3/10 AQAAA. G v I "Y- 519% PbZrO 32, E PbTiO TNVE R S Mi/suo 050 Osarnu Kuman To'lsuyo M'shimo/o June 12, 1973 rrsuo OSADA ET AL 3,738,936

FERROELECTRIC AND PIEZOELECTRIC COMPOSITION Filed March 4, 1971 2 Sheets-Sheet 2 Variation in The Longitudinal Coupling Coefficient (K )And The Dielectric 2000- Constant (E) Versus Pb(ln'/ Nb'/ O -PbTi O Concentration 5O 4O 3O 20 [500 a Variation In The Longitudinal Coupling Coefficient (K And The Dielectric Constant (E)Versus PbTiO .PbZrO 5O Concentration [Pb(ln Nb 0 O Constant At lOmols X= lOmoI 30 4O 5O "-PbTiO INVENTORS 60 5O 4O PbZrO Mi/suo 05000 moi 080ml! Kumon Tq/sizya M's/u'ma/o United States Patent 01 hoe The portion of the term oi the patent subsequent to Dec. 28, 1988, has been disclaimed Int. Cl. C04b 35/46, 35/48 US. Cl. 252-623 8 Claims ABSTRACT OF THE DISCLOSURE Ferroelectric and piezoelectric compositions consisting essentially of a solid solution of the ternary system XPb (InNb) O -Y(PbZrO )-Z(PbTiO wherein from 0 to 25 atomic percent of the PM is replaced by an alkaline earth metal is disclosed. The constituents are defined by the formula wherein X, Y and Z are in the following ranges, taken with reference to the figure ABCDEFGH in FIG. 1:

X Y Z Also disclosed is a binary system consisting of from 55 to 75 mole percent Pb(InNb) O and from 45 to 25 mole percent PbTiO wherein from 0 to 25 atomic percent of the Pb+ is replaced by an alkaline earth metal.

CROSS-REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of Ser. No. 712,192, filed Mar. 11, 1968, entitled Ferroelectric and Piezoelectric Composition, by the same inventors as the present application, and now US. Pat. No. 3,630,908.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to a novel ferroelectric and piezoelectric composition.

Description of the prior art Ferroelectric and piezoelectric materials containing barium titanate, lead titanate zirconate and the like as their principal constituents are used in many diverse applications, such as transducers useful in devices such as wave filters for producing or sensing vibrations, elements for generating high voltage and the like.

Patented June 12, 1973 SUMMARY OF THE INVENTION The present invention provides a ferroelectric and piezoelectric material having a novel composition consisting essentially of a solid solution of a ternary system consisting of Pb(*InNb) O PbTiO and PbZrO in the amounts shown above, wherein from 0 to 25 atomic percent of the Pb+ is replaced by an alkaline earth metal.

The present invention also contemplates a ferroelectric and piezoelectric composition consisting essentially of a solid solution of a binary system consisting of from about 55 to about mole percent P b(InNb) O and from about 45 to about 25 mole percent PbTiO wherein from 0 to 25 atomic percent of the Pb+ is replaced by an alkaline earth metal.

A ferroelectric and piezoelectric material prepared in accordance with the present invention is characterized by intense 'ferroelectric and piezoelectric properties which are obtained by applying a DC voltage to a sintered ceramic material in the same manner by which ceramics of barium titanate or lead titanate zirconate are made, thereby polarizing the ceramic and providing a residual polarization to the ceramic. This property enables the ceramic to be advantageously used in transducers in all types of electrical devices.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a triangular compositional diagram illustrating the various embodiments of the present invention.

FIG. 2 is a diagram illustrating curves which indicate variations in the longitudinal coupling coefficient and the dielectric constant, respectively, of the material produced in accordance with the present invention when the ratio of lead titanate with respect to lead indate niobate is varied.

FIG. 3 is a diagram illustrating the curves which indicate the variation in the longitudinal coupling coetficient and the dielectric constant, respectively, of the material produced in accordance with the present invention when the ratio of lead titanate with respect to lead zirconate is varied and the content of lead indate niobate in the material is held to 10 mole percent.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The material produced in accordance with the present invention is composed of with from 0 to 25 atomic percent of the P13 being replaced with an alkaline earth metal.

All of the ceramics made of the ternary system in accordance with the present invention possess piezoelectric properties. However, from the viewpoint of industrial interest, the subject matter of the present invention is dirooted to the following range of each constituent of the material referred to in the diagram in FIG. 1:

Y-PbTiO Mole percent X 5-75 Y 25-55 Z 0-60 wherein X Y+Z= 1 00,

The values of the coupling coefiicient k;;;; and the dielectric constant e of the material are maximums at positions adjacent to the phase boundaries of PbTiO and PbZrO in the ternary system shown in FIG. 1, i.e., the above values are maximum when the content mole percent of each constituent is to fall on the lines connecting each of the middle points of sample numbers 19-23, 1822, 16-21, 1520, and 4-5 in FIG. 1. The above values decreases as the composition of the material is varied from the above described regions. From an industrial viewpoint, the preferred boundary is selected in the present invention to conform to the numerals A-B-C and E-F-G-H in FIG. 1.

The composition of the material containing is superior from the viewpoint of ease of sintering and polarization of the material in comparison with the binary system consisting of PbTiO PbZrO Further, the Curie point of the composition containing Pb(InNb) O is higher than that of the composition which does not contain Pb (InNb) O The Curie point of composition sample number 16 is about 50 C. higher than that of a binary system in which the ratio of Zr to Ti is kept at about the same ratio as that of sample number 16. Accordingly, the lower limit of the composition wherein the inclusion of Pb(InNb) O is recognized to give advantageous results is represented by the numerals C-D-E-F in FIG. 1.

In preparing the ceramic in accordance with the present invention, oxides such as In O Nb O TiO ZrO and the carbonates of the peroxides thereof which can easily be decomposed by heating to form the oxides may be utilized as raw materials. Since ZrO usually contains a small amount of hafnium, it is possible to replace Zr by hafnium in the present invention. However, since hafnium is expensive in comparison with Zr, the selection of the constituents should be made from an industrial viewpoint.

EXAMPLE The oxides in Table 1 were used as raw materials in powdered form since these were commercially available at a purity greater than 99.5%. The oxides were mixed together after each of the oxides was weighed to obtain the weight ratio shown in Table 1. The mixture was then dried, and heated at 800 C. for two hours so as to effect a temporary sinterin g thereof.

The temporarily sintered material was coarsely crushed, finely powdered and wet blended in a ball mill for hours.

After the powdering and blending, an organic caking agent was added to the powder, and the thus prepared mixture was pressed so as to form a cylindrical shape having a diameter of 6 mm. and a length of 18 mm. The thus formed body was sintered in a platinum casing at a temperature ranging from 1230 to 1270 C. for three hours within an atmosphere of lead. The sintered body was ground into a shape having a diameter of 5 mm. and a length of 15 mm. with the opposite ends of the body being glazed with silver paint.

The thus-formed element was polarized by applying a DC voltage of 2.5 kv./mm. in silicone oil at a temperature of 100 C. After the expiration of 100 hours from the time of polarization of the element, the physical properties of the element were measured by the methods defined by the IRE standard. Table 1 shows the test results, the longitudinal coupling coefficient being indicated by k;,;;, and the dielectric constant being indicated by e. The variation in properties due to the change in the ratio of Pb(InNb) O with respect to PbTiO is shown in FIG. 2. The variation in the properties due to the change in the ratio of P ith r p t to Pb i when he c011.-

tent of Pb(InNb) O is kept at 10 mole percent is shown in FIG. 3.

TABLE 1 Composition-Properties (refer to Fig. 1)

Composition, mole percent Sinterlng temp., a,

Pb(InNb) .503 PbTiO; PbZrO; percent a Sample numbers 2-6 and 9-28 are included within the claims, whereas sample numbers 1, 7, 8 and 29-33 are excluded from the claims for the previously mentioned reasons though they also illustrate the piezoelectric properties.

It is well known in the art that mechanical losses in a ceramic composed of the ternary system can be reduced, and the dielectric constant thereof increased, by replacing a portion of the Pb+ with an alkaline earth metal. A similar efiect can be obtained in the ternary system produced in accordance with the present invention by replacing a part of the Pb+ with an alkaline earth metal.

Accordingly, from 0 to 25 atomic percent of the Pb+ in the composition of the present invention is replaced with an alkaline earth metal. Any of the alkaline earth metals can be employed, with strontium, barium, calcium and mixtures thereof being preferred.

The following Table 2 shows the increased dielectric constant of the composition of the present invention when a portion of the Pb is partially replaced with an alkaline earth metal. In Table 2, k represents the longitudinal coupling coefiicient and 6 represents the dielectric con- What is claimed is:

1. A ferroelectric and piezoelectric composition consisting essentially of a solid solution of a binary system consisting of from about 55 to about 75 mole percent Pb(InNb) O and from about 45 to about 25 mole percent PbTiO wherein a portion of up to 25 atomic percent of the Pb+ in said composition is replaced by an alkaline earth metal, said portion being an amount sufficient to increase the dielectric constant of said composition.

2. The composition of claim 1 wherein said alkaline earth metal is strontium, barium, calcium or mixtures thereof.

3. A ferroelectric and piezoelectric composition consisting essentially of a solid solution of a ternary system consisting of about mole percent Pb(InNb) O from about 45 to about 50 mole percent PbZrO and from about 40 to about 45 mole percent PbTiO with the total mole percent being 100 percent, and wherein a portion of up to 25 atomic percent of the Pb+ is replaced by an alkaline earth metal, said portion being an amount sufficient to increase the dielectric constant of said composition.

4. The composition of claim 3 wherein said alkaline earth metal is strontium, barium, calcium or mixtures thereof.

5. A ferroelectric and piezoelectric composition consisting essentially of a solid solution of a ternary system consisting of about 30 mole percent Pb(InNb) O from about 25 to about 30 mole percent PbZrO and from 6 about to about mole percent PbTiO with the total mole percent being 100 percent, and wherein a portion of up to 25 atomic percent of the Pb+ is replaced by an alkaline earth metal, said portion being an amount sufiicient to increase the dielectric constant of said composition.

6. The composition of claim 5 wherein said alkaline earth metal is strontium, barium, calcium or mixtures thereof.

7. A ferroelectric and piezoelectric composition consisting essentially of a solid solution of a ternary system consisting of about mole percent Pb(InNb) O from about 5 to about 10 mole percent PbZrO and from about 40 to about 45 mole percent PbTiO with the total mole percent being percent, and wherein a portion of up to 25 atomic percent of the PM is replaced by an alkaline earth metal, said portion being an amount suffi cient to increase the dielectric constant of said composition.

8. The composition of claim 7 wherein said alkaline earth metal is strontium, barium, calcium or mixtures thereof.

References Cited UNITED STATES PATENTS 3,468,800 9/1969 Yokoyama et a1. 252*629 3,472,779 10/1969 Kurihara et a1 252-62.9

OSCAR R. VERTIZ, Primary Examiner I. COOPER, Assistant Examiner 

